Antenna system for ils localizers



June 30, 1970 o. P. HAKONSEN ANTENNA SYSTEM FOR ILS LOCALIZERS 3 Sheets-Sheet 1 Filed June 4. 1968 INVENTOR.

OLE PETTER H KONSED ATTORNEYS June 30, 1970 o. P. HAKONSEN 3,518,673

ANTENNA SYSTEM FOR ILS LOCALIZERS Filed June 4, 1968 3 Sheets-Sheet 2 E I\ W &

INVENTOR.

OLE PETTER HAKONSEN ATTORNEYS June 30, 1970 o. P. HAKQNSEN ANTENNA SYSTEM FOR ILS LOCALIZERS 3 Sheets-Sheet 5 Filed June 4, 1968 m QE INVENTOR.

OLE PETTER HAKONSEN BY W ATTORNEYS United States Patent Int. c1. G015 1/16; H01q 11/10 US. Cl. 343-108 7 Claims ABSTRACT OF THE DISCLOSURE Antenna system for ILS localizers adapted to have sufiicient backward radiation for course information backwardly from the runway, with different course sector widths forwardly and backwardly, the elementary antennas of the system having different front-to-back ratios.

This invention relates to an improvement of antenna systems for the localizer section in instrument landing systems (ILS) for airports. This kind of antenna systems is composed of a number of separate antennas and is located adjacent the end of the runway which shall be covered by the localizer.

It is frequently desirable that the antenna system has some radiation also in a direction backwardly with respect to the runway, so that the airplanes if necessary can receive course information in positions backwardly from the runway. It is known in connection with such antenna systems to arrange the same so that different course sector widths can be obtained forwardly and backwardly, respectively, viz so that the back course sector width is larger than the front course sector width. The larger back course sector width is desirable because the area covered out from the direction of the runway is larger, and feasible because the requirements as to exactitude are not so strict as in the forward direction.

It is the object of this invention to provide a new antenna system which is a more simple and inexpensive way than the existing systems makes possible different front and back course sector widths together with an exact and controllable adjustment of the relations and conditions wanted in each practical case.

In known antenna systems for ILS localizers there are used separate antennas directed backwardly from the runway so as to obtain the desired backward radiation. Thus, such a solution is the only possible in a known system in which dipoles arranged in front of a metal wire net are used as main antennas. Such an arrangement will give too small or no radiation at all backwardly, so that no course information can be obtained in that direction. Another complication with such conventional systems is that the separate antennas for the backward direction require special equipment for a suitable feeding thereof.

The solution provided by the present invention is based on the utilisation of separate antennas which can give a certain backward radiation. The feature which in the first place is characteristic of the antenna system according to the invention is that the separate or elementary antennas in the system have different front-to-back ratio.

With the solution according to the invention it has been found most practical to modify only some of those antennas which are located outermost in the system, i.e. with the largest distances from the centre line. In many instances it will be sufficient only to modify the outer- \most antenna on each side. For obtaining an increased course sector width in a backward direction it is necessary to modify these outermost antennas in such a way that their backward radiation becomes smaller. In this connection it is of interest to note that with the actual types 3,518,673 Patented June 30, 1970 'ice of separate antennas-and in particular with the preferred logperiodic dipole antennas-the forward radiation will not be noticeably influenced by the change of the backward radiation in this 'way.

Even though this invention most advantageously employs logperiodic antennas as the separate antennas of the system, the same is not limited to this type of antenna. Another antenna type which can be used is the Yagi antenna. This latter type of antenna, however, has the inconvenience in this connection that thus far it has not been possible to calculate the same exactly on beforehand for attainment of requirements which have been set, for instance with respect to the front-to-back ratio. The adjustment in each case must be carried out experimentally and this can be both costly and time-consuming.

With separate antennas in the form of logperiodic dipole antennas which is preferred according to the inventionthe different front-to-back ratios are preferably obtained thereby that one or more dipoles in preferably each logperiodic dipole antenna have a length and/or a position along the feed line which involves deviation from an exact logperiodic structure. Such deviations can be determined comparatively quickly and securely because the logperiodic structure or construction can be described quite exactly by mathematical methods. But modification of the position of dipoles along the feed line the same are displaced in parallel in the longitudinal direction of the feed line.

More specifically it is according to the invention found practical that the length and/or position of one or more dipoles deviate with a maximum of 30 percent from an exact logperiodic structure.

Further, the antenna system according to the inven tion is preferably made in such a way that a maximum of one fifth of the total number of dipoles have a length and/ or position which deviates from an exact logperiodic structure.

The fact that it is preferred to employ logperiodic separate antennas in the system according to the invention has for reason not only that this type of antenna can be treated mathematically, but also that logperiodic antennas are little influenced by weather and rain or snow conditions, for instance thick snow layers. For further improvement of the characteristics in this respect it is advantageous to encase the feed line with a weather resistant dielectric, for instance a plastic material, such as fibreglass reinforced polyester.

For a closer explanation of the invention the same is described below with reference to the drawings.

FIG. 1 shows diagrammatically and simplified a plan view of an antenna system according to the invention with radiation patterns indicated. FIG. 2 shows a plan view of a logperiodic dipole antenna with deviation from the exact logperiodic structure.

FIG. 3 is a diagram of an exact logperiodic structure.

The antenna system of FIG. 1 is composed of six separate antennas 1-6, for instance logperiodic dipole antennas, which are arranged side by side along a line T which forms a right angle with the centre line S of the runway. As known per se, the antenna arrangement is symmetric about the centre line S. With full lines there is for each separate antenna indicated a radiation pattern comprising a forward lobe 1c, 20, and so on, respectively, and a backward lobe 1a, 2a, 3a, 4a, 5a, and 6a, respectively. For the antennas 1, 2, 5, and 6which are the two outermost antennas on each side in the system-there is further with dotted lines indicated backward lobes 1b, 2b, 5b, and 6b, which are different from the backward lobes 3a and 4a. The antennas 1, 2, 5, and 6 are according to the invention modified in such a way that their initial backward lobes 1a, 2a, and so on, have been changed to those lobes 1b, 2b, 5b, and 6b which are shown with dotted lines, so that the radiation in the backward direction has become smaller compared to the forward radiation, i.e. the front-to-back ratio has become greater. It is then presumed that the forward radiation has not been noticeably influenced by the modification of these antennas.

In FIG. 1 there is further with the lines 1 1' and 11" indicated an angle C in the forward direction. This angle shall illustrate the course sector width in the forward direction. Backwardly there is in a corresponding way shown a course sector width with the angle A between the lines 13 and 13", and a course sector width B between the lines 12' and 12". The course sector width A is the one obtained when all separate or elementary antennas have the same front-to-back ratio, i.e. when none of the separate antennas are modified as explained above. In this case the course sector width in the forward direction is equal to the course sector width backwardly, i.e. A=C.

If, however, the antennas 1, 2, 5, and 6 are modified as explained so that their backward lobes are as indicated 'with dotted lines, the course sector width backwardly 'will become greater, which is shown with the angle B in FIG. 1.

In FIG. 2 there is shown an example of a type of separate or elementary antenna which can be used in the antenna system according to the invention. In this figure there is shown a logperiodic dipole antenna 20 with seven dipole elements .21-27 mounted on the feed line 28. Since the antenna is symmetrical only one half thereof has been included in the drawing. Dipole element number five from the front (the element 25) is here made shorter than what would have been required in an exact logperiodic structure, and this leads to a modification of the kind discussed above. Such a deviation from the exact logperiodic structure has for result that the antenna which in its normal construction has quite negligible backward radiation-becomes a noticeable backward ra diation which is utilised in the antenna system according to the invention. Thus, by employment of such a logperiodic antenna in the system of FIG. 1, preferably all antennas will deviate from the strict logperiodic principle, but the two outermost antennas on each side are modified diflerently from the two central antennas, viz in such a way that their backward lobes are smaller than those of the latter antennas. In this way there is according to the invention simply and inexpensively obtained a change of the back course sector width with respect to the front course sector width.

An exact logperiodic structure is shown on FIG. 3. The extremes of the dipoles are bounded by an angle a and the distances from a virtual centre 0 are defined by the constant parameter -r and the radius R A change in dipole length and/or the distance from the dipole to the virtual center 0 is defined as a deviation from the exact logperiodic structure.

As an example of what can be obtained it may be mentioned that with a shortening of said element 25 in the antenna 20 with about 12 percent, the front-to-back ratio will decrease from a normal-and negligiblevalue (exact logperiodic structure) of about 30 db, to about 13 db. Shortening of such an element by other percentages will give corresponding variations in the front-to-back ratio.

With six identical elementary antennas having a frontto-back ratio of 13 db in the system shown in FIG. 1, one will for instance have a front course sector width of about 4 equal to the back course sector width (A=C=about 4). If the two outermost antennas on each side, i.e. the antennas 1, 2, 5, and 6 are modified in such a way that their front-to-back ratio becomes about 19 4 db, the back course sector width will for instance increase to about 7 The ILS localizer referred to in the specification and claims is defined in the Aeronautical Telecommunications, Annex 10 of the International Civil Aviation Organization .(ICAO) It is obvious that the invention is not limited to the embodiments shown in the drawing and the above ex ample. Even if normally it will be desirable to have a larger back course sector width than front course sector width, the opposite will also easily be obtainable with the solution provided by the invention. With particular reference to logperiodic dipole antennas it is on the basis of the above description further obvious to an expert in this field that in addition to variation of the length of the antenna elements, variation of the position of the elements along the feed line can also be used to obtain said deviations from the exact logperiodic structure. According to the invention it is found that such length or position deviations of up to 30 percent can be utilised with advantage in practice. Likewise it has been found practical that up to a maximum of one fifth of the total number of dipole elements can be used for such modifications of this type of antenna.

I claim:

1. Antenna system for an ILS localizer comprising a plurality of elementary antennas located adjacent the end of the runway covered by the localizer, means producing sufiicient radiation and course information in a direction backwardly from the runway having difierent course sector widths forwardly and backwardly and said elementary antennas of the system having different frontto-back ratios.

2. Antenna system according to claim 1 wherein said elementary antennas have the form of logperiodic dipole antennas with at least one dipole in each logperiodic dipole antenna having a length along the feed line which involves a deviation from an exact logperiodic structure.

3. Antenna system according to claim 1 wherein said elementary antennas have the form of logperiodic dipole antennas with at least one dipole in each logperiodic dipole antenna having a position along the feed line which involves a deviation from an exact logperiodic structure.

4. Antenna system according to claim 2 wherein said length deviates with a maximum of 30 percent from an exact logperiodic structure.

5. Antenna system according to claim 3 wherein said position deviates with a maximum of 30 percent from at exact logperiodic structure.

6. Antenna system according to claim 2 wherein a maxi mum of one fifth of the total number of said dipoles has a length which deviate from an exact logperiodic structure.

7. Antenna system according to claim 3 wherein a maximum of one fifth of the total number of saiddipoles has a position which deviate from an exact logperiodic structure.

References Cited UNITED STATES PATENTS 2,593,485 4/ 1952 Pickles 343-107 2,993,665 7/1961 Carpenter 343-107 X 3,147,479 9/1964 Williams 343792.5 3,257,661 6/1966 Tanner 343792.5 3,283,325 11/1966 Jones 343109 2,513,493 7/ 1950 Kliever 343-107 RODNEY D. BENNETT, Primary Examiner T. H. TUBBESING, Assistant Examiner US. Cl. X.R. 343792.5, 853 

